Sound absorber

ABSTRACT

A sound absorber for jet engines and the like including a housing defining an inflow opening and an outflow opening. Sound absorbing elements positioned within the housing define substantially parallel entrance and exit planes. The sound absorbing elements include a plurality of gas guidance and baffle elements in two spaced-apart and parallel row-like arrangements, the elements having U-shaped, V-shaped, or semicircular cross-sections. The rows of sound absorbing elements are offset and the elements arranged such that the opened cross-sectional areas face each other in overlapping fashion. The entrance plane and the exit plane are inclined relative to an entrance flow through the inflow opening within an angular range of between 0° to less than 90°. The flow into the sound absorber is divided into first partial flows between adjacent sound absorbing elements, whereupon each first partial flow splits into two second partial flows each of which merge with an adjacent second partial flow to form common a third partial flow directed toward the exit plane.

FIELD OF THE INVENTION

The present invention relates to a sound absorber consisting of one or aplurality of sound absorbing elements which are installed in a round oroval guidance channel through which a flow acted upon by sound extends.

BACKGROUND OF THE INVENTION

Such devices are, for instance, known as exhaust systems on engines orair guides of air conditioning systems. In such systems a soundinsulation is achieved by arranging "baffle plates" in the guidancechannel (reflection damping) or by perforating the guidance channel andsimultaneous covering with sound-absorbing materials (such as rock wool)between perforated guide pipe and another gas-tight covering (absorptiondamping).

In these systems a satisfactory sound absorption can only beaccomplished at great overall lengths and thus at great amounts ofmaterial and great weights.

The present invention is based on the utility model registered underRegister No. G 92 10 988.8 for a sound absorbing device for rectangularcross-sections.

SUMMARY OF THE INVENTION

It is the object of the present invention to improve a sound absorber insuch a manner that an increased sound absorption can be achieved withthe efforts spent on space, material and weight being small.

It is also the object of the present invention to provide a soundabsorber of the above-mentioned type which avoids the drawbacks of theprior art and nevertheless has a small size under optimized flowconditions, at a high absorbing performance and at an optimized exhaustgas counterpressure.

In accordance with the invention, the object is attained by providing asound absorber with a housing having inflow and outflow openings andsound absorbing elements therebetween. The sound absorbing elementsdefine parallel entrance and exit planes inclined at an angle of lessthan 90° with respect to a flow through the inflow opening.

The invention is especially suited for sound absorbing measures insystems in which there is little space available and whose weights arerestricted and in which, at the same time, the maximum pressure islimited at a given throughput.

The sound absorber known from utility model 92 10 988.8 has only alimited absorbing effect, since the entrance flow impinges at a rightangle onto the entrance plane. This may lead to undesired reflections ofthe sound waves and may be detrimental to the flow characteristics.Another disadvantage is that only rectangular cross-sections can berealized in the prior-art sound absorber. By contrast, the inventionmakes it possible to guide the entrance flow at a flat angle against theentrance plane. This will effect substantially improved sound absorbingcharacteristics which are above all due to the improved flowcharacteristics. In addition, it is possible to give the sound absorbera smaller size or to install a larger number of sound absorbing elementswithin a given volume.

These demands are, for instance, made on sound absorbers of aircraftengines which have a critical weight and in which there is only a verylimited space available within the engine covering. Moreover, the soundabsorber should only produce a limited back-pressure towards the engine.

Conventional systems (absorption dampers) must be mounted outside of theengine covering because of their large dimensions, they are veryobjectionable from an aerodynamic point of view and heavy.

Making use of the present invention on the sound absorber of an aircraftand integrating an absorbing element with a weight of 0.5 kg, a diameterof 95 mm, and a length of 200 mm into the existing exhaust system, onewill achieve an absorbing performance which is improved by 1.5 dB(A) incomparison with a conventional external sound absorbing system having aweight of about 6 kg and a diameter of about 15 cm and a length of 1 m.

This comparison is based on officially acknowledged measurement results.

The improved sound-absorbing effect of the invention is due to thedesign of the gas guiding channels which respectively unite acousticallyidentical gas flows in the opposite direction by way of their innercontour and simultaneously form optimum reflection surfaces due to theirconcave outer contours.

The sound absorber of the invention shows the same degree of soundabsorption as compared with conventional systems (reflection,absorption) with considerably smaller efforts being spent on space,weight and material, or a considerably improved sound absorption isachieved under the same efforts.

By arranging the entrance and exit planes on cylindrical or conicalsurfaces, the present invention permits any adaptation of the radial andlateral dimensions of the flow guiding channel to the secondaryconditions made by pressure and throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be described with reference to embodimentsillustrated in the drawing, in which:

FIG. 1 is a lateral view of a flow guidance channel with a soundabsorbing element arranged conically relative to the flow direction;

FIG. 2 is a lateral view of a flow guidance channel with entrance plane3 and exit plane 4 arranged in parallel with the inflow direction;

FIG. 3 is a lateral view of a flow guidance channel with entrance plane3 and exit plane 4 arranged in parallel with the inflow direction withtwo inflow openings arranged at the same level and a radial outflowopening;

FIG. 4 is an enlarged and straightened radial section of the soundabsorbing element of FIG. 1, FIG. 2, and FIG. 3 and taken along lineA--A of FIGS. 1, 2 or 3;

FIG. 5 is a variant of the sound absorbing element illustrated as aradial section by analogy with FIG. 4 and taken along line A--A of FIGS.1, 2 or 3;

FIG. 6 is a further variant of the sound absorbing element, representedas a radial section by analogy with FIGS. 4 and 5 and taken along lineA--A of FIGS. 1, 2 or 3; and

FIG. 7 is a radial section through a sound absorber according to FIG. 2and FIG. 3 with a cylindrical absorbing element of the type illustratedin FIG. 4 and taken along line B--B of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross-sectional view through a typical exhaust system. Inthe embodiment in a sound absorbing element 2 is conically mountedwithin an enlarged round cross-section relative to the entrance flow 5.The area of the absorbing element 2 which is flown through can beadapted to the prevailing space and pressure conditions by varying thecone angle of the absorbing element 2.

FIG. 2 is a sectional view through a typical exhaust system in which theentrance flow 5 and the exit flow 10 are located along a common line.The absorbing element 2 has a cylindrical shape and is radially flownthrough from the outside to the inside.

An adaptation to the prevailing space and pressure conditions ispossible by varying the length of the absorbing element 2.

FIG. 3 is a sectional view through a typical exhaust system in which twolateral entrance flows 5 are arranged along a common line. The exit flow20 as drawn is at a right angle relative to the entrance flow 5. One ora plurality of outflow openings can be provided on the outer casing 11at any desired angle. The absorbing element 2 has a cylindrical shapeand is radially flown through from the inside to the outside.

Any adaptation to the prevailing space and pressure conditions ispossible by varying the length of the absorbing element 2.

FIG. 4, FIG. 5 and FIG. 6 are radial sectional views through theentrance plane 3 and the exit plane 4 and the guidance channels 7 formedby the two planes. Between the entrance and exit planes 3, 4, aplurality of gas guidance and baffle elements are positioned. A firstrow of elements 12a are U-shaped, V-shaped or semicircular incross-section and open away from the entrance plane 3. A second row ofsimilarly shaped elements 12b open away from the exit plane toward thefirst row of elements 12a. The rows of elements 12a, 12b are spacedapart and offset with respect to each other so that the open sides faceeach other in overlapping fashion.

The sound of the entrance flow 5 which hits upon the entrance plane islargely reflected from the outer surface of the entrance plane, and theentrance flow 5 is divided into a plurality of first partial flows 6upon passage through the entrance plane 3.

The flow channels 7 which are formed by the entrance plane 3 and theexit plane 4 divide the first partial flows 6 respectively into twofurther second partial flows 8.

In the further course of the flow channels 7 two second partial flows 8which have been created by the division of adjacent first partial flows6 are respectively guided towards each other in the opposite direction,thereby forming one third partial flow 9.

A virtual baffle wall is created by uniting two acoustically identicalflows in opposite direction, whereby noise is considerably reduced.

The third partial flows 9 are guided through the exit plane 4 into theflow guidance channel 1 and are combined to form outlet flow 10.

The sides of the exit plane 4 which face away from the exit flow 10 formthe ideal aerodynamic shape for producing a uniformly mixed deceleratedflow.

FIG. 7 is a sectional view through an exhaust gas system according toFIG. 2 and FIG. 3, with the entrance plane 3 and exit plane 4 inparallel with entrance flow 5, and of the air guide type shown in FIG.4.

Designations:

1=flow guidance channel

2=sound absorbing element

3=entrance plane

4=exit plane

5=entrance flow

6=first partial flow

7=guidance channel

8=second partial flow

9=third partial flow

10=exit flow

11=outer casing

12a=first plurality of baffle elements

12b=second plurality of baffle elements

A=radial displacement of the entrance plane 3 and the exit plane 4

B=lateral displacement of the entrance plane 3 and the exit plane 4

A--A=sectional plane (partial section through an absorbing element)

B--B=sectional plane (overall section)

I claim:
 1. A sound absorber, comprising:an outer housing having atleast one inflow opening and at least one outflow opening, said housingbeing adapted to receive a noisy flow of gas entering said housing alongan axis through said inflow opening, and exiting said housing throughsaid outflow opening; a sound-absorbing element positioned in saidhousing between said inflow opening and said outflow opening, saidsound-absorbing element defining an entrance plane with a substantiallyunimpeded path to said inflow opening and an exit plane with asubstantially unimpeded path to said outflow opening, said entrance andexit planes being substantially parallel with respect to one another;and a plurality of baffle elements arranged in two spaced-apart rows,said baffle elements being U-shaped, V-shaped or semicircular incross-section so as to each have an open side, a first row of saidbaffle elements being positioned adjacent said entrance plane andopening away from said entrance plane, and a second row of said baffleelements being positioned adjacent said exit plane and opening away fromsaid exit plane toward the first row of elements, the two rows ofelements being offset with respect to one another so that the openedsides of the baffle elements face each other in overlapping fashion, andwherein said sound-absorbing element is positioned such that saidparallel entrance and exit planes are inclined at an angle of between 0°to less than 90° relative to the axis of flow of said noisy flow throughsaid inflow opening.
 2. The sound absorber of claim 1, wherein saidsound-absorbing element is formed in a cone shape so that said entranceplane and said exit plane form spaced-apart conical surfaces.
 3. Thesound absorber of claim 2, wherein an apex of said cone faces towardsaid inflow opening.
 4. The sound absorber of claim 1, wherein saidsound-absorbing element is formed as a cylinder so that said entranceplane and said exit plane form spaced-apart cylindrical surfaces havinga common axis aligned with said noisy flow through said inflow opening,said sound absorber being formed so that the noisy flow passes radiallythrough said sound-absorbing element toward said outflow opening.
 5. Thesound absorber of claim 4, wherein said housing and said sound-absorbingelement are arranged so that the noisy flow passes radially inwardthrough said sound-absorbing element toward said outflow opening.
 6. Thesound absorber of claim 4, wherein said housing and said sound-absorbingelement are arranged so that the noisy flow passes radially outwardthrough said sound-absorbing element toward said outflow opening.
 7. Thesound absorber of claim 1, wherein said baffle elements of said firstrow are spaced apart to form flow dividers adjacent said entrance planedividing said noisy flow into first partial flows therebetween, saidbaffle elements in said second row positioned to divert said firstpartial flows into two divergent second partial flows directed generallytoward the baffle elements in said first row, and the baffle elements insaid first row positioned to further divert adjacent second partialflows into a common third partial flow directed between baffle elementsin said second row and toward said exit plane.
 8. The sound absorber ofclaim 7, wherein the baffle elements in the first and second rows ofsaid sound-absorbing element are symmetrically arranged such that asimilar division of flow occurs regardless of the direction of saidnoisy flow, either from said entrance plane to said exit plane, or fromsaid exit plane to said entrance plane.